50 F. A. BATHER, CRINOIDEA OF GOTLAND. 



It is chiefly by means of English speeimens in the British Museum that this species 

 has been studied. The Gotland speeimens are two small, closely-coiled steins (a and b), 

 and it is to them that the present description is confined. The trivial narae is due to the 

 close superficial resemblance of the coiled stem to a »Cornu Ammonis». 



Description. 



In specimen a the longest diameter of the total coil is 19 mm.; the shortest dia- 

 meter is 13.5 mm. The coil in all speeimens is closely involute, as in H. convolutus, 

 and, perhaps as a consequence of this, the inner side is more eoneave than in H. Fletcheri. 



In specimen a, in the distal region of the stem 7 ossieles go to o mm., hut higher 

 up 6 go to 5 mm. In the same specimen the width of the stem in the distal region is 

 3.5 mm., while higher up it is 4.5 mm.; the sections of the ossieles are also different, as 

 in H. convolutus (tigs. 54, 56): this may point to a semi-free existence. The cirriferous 

 ossieles decrease in height towards the inner curve very slightly, if at all; the plain ossi- 

 eles decrease much more: thus the mean height decreases a £ood deal. 



It appears that the cirri are never paired on successive ossieles in this species. In 

 place of this there are two main plans of arrangeinent, which in the British speeimens 

 seem to l»e fairly distinct and according to which one may place the speeimens in one of 

 the two following varicties. 



var. h ijugicirrus. 



Cirri regularly paired on alternate colunmals. 



British Museum speeimens 338, E 323, E 356, E 415, E 1326, and 

 E 1410 6. 



ri/r. alternicirrus. 



Cirri regularly alternating, one on each columnal. 



British Museum speeimens 57091, 57207, E 355 and E 1410 a, and 

 Gotland specimen b. 



In both of these varieties the height of each columnal, as measured on the outer 

 curve, is the same (tig. 53); and in both varieties the stem, as seen from the side, pre- 

 sents the same appearance (fig. 51). It is only on the inner curve of the stem that anv 

 difference is apparent. Here in TI. bijugicirrus the cirriferous colunmals have an hour- 

 glass or dumb-bell outline and meet one another almost if not entirely, so that the plain 

 colunmals are partly ludden and have a lenticular outline. In H. alternicirrus, from the 

 same point of view. each ossicle is wedge-shaped and bears a eirrus at its broader end 

 (fig. 57). 



These varieties might be separated as species, were it not for the evideneo of spe- 

 cimen a. This, which is in the main eonstrueted on the bijugicirrus plan, shows in its 

 distal region and elsewhere a few ossieles of the alternicirrus type. Since the varieties 

 are in all other respects the same, and since it is a diftieult matter to distinguish them, 

 advantage may be taken of this eonnecting form to retain them under one specific nanie. 



The cirri are short, being at most 6 mm. in length, and are eomposed of few 

 ossieles, usually only 3 or 4. The proximal cirral is about 1.9 mm. long: subsequent 



